This invention relates to a needle, particularly for industrial embroidery machines and is of the type which has a shank and a blade adjoining the shank. The blade terminates in a tapered portion (cone) ending in a point and has at least one groove and an eye. The blade is provided, in the vicinity of the shank, with a weakened portion defining a predetermined breaking location.
Industrial embroidery machines, such as Schiffli machines and automatic multihead embroidery machines may have a length of approximately 19 m and may be provided with up to 1418 needles. In case a needle is bent or breaks, the embroidery pattern shifts or is severely damaged. In any event, the machine has to be stopped for replacing the needle. Also, the damage is substantial because a corresponding strip of the embroidery base has to be excised over the entire width of up to 19 m.
To avoid an elastic deformation (bending) of the needles during the embroidery process, frequently needles are selected which have a thickness greater than that which the embroidery base can tolerate. This leads to tears in the fabric or the thread. Also, the needles have to be relatively brittle as the result of the hardening process. This, however, increases the risks of needle breakage. While needle breakage is essentially highly undesirable, when it occurs, it should take place in the vicinity of the shank to ensure that the remaining needle stump cannot penetrate into the embroidery base and thus damage the base or the already-produced embroidery patterns.
Also it is desirable that the needle breaks before it is permanently deformed.
As disclosed in German Offenlegungsschrift (application published without examination) 4,320,956, it is known to provide machine needles with a predetermined breaking location formed as a groove or notches or slender bore holes which are provided in the cone below the shank and which may also be present in the region of the blade. Such grooves provided by material removal or notches and slender bores provided by laser beam processes, as well as the tendency of crack-formation in these structures, however, reduce the breakage resistance and thus the service life of the needle to an undesired extent. Consequently, such needles may be used only under restricted conditions.